The present invention is a method for making a triarylamine compound having hydrocarbonoxysily groups, which is useful in charge transfer materials and the like used in photosensitive materials for electronic photography. Triarylamines are important materials as charge transfer substances and in particular those having hydrocarbonoxysilyl groups have the following advantages over those not having hydrocarbonoxysilyl groups: (1) the characteristics attributable to the hydrocarbonoxysilyl groups are imparted to the surface characteristics of a charge transfer material, (2) miscibility with silicon-based materials is good, (3) silicon-oxygen bonds are easier to form on an inorganic material surface, and (4) it is possible to effect curing by the formation of a crosslinked structure resulting from silicon-oxygen bonds.
The following are the most common methods for manufacturing a triarylamine having hydrocarbonoxysilyl groups.
1) Organometal reagent method: This process includes a Grignard method in which an organometal reagent is prepared by a reaction between a halogen derivative of a triarylamine and metallic magnesium and this product is allowed to react with chlorosilane or an alkoxysilane to form silicon-oxygen bonds; and an organolithium method in which a lithium reagent is used in place of the above-mentioned metallic magnesium.
2) Hydrosilylation method: One such hydrosilylation method involves allowing a triarylamine having unsaturated groups to react with a hydride silane compound to form silicon-oxygen bonds.
In method 1 above a Grignard method is particularly common, but has the following problems:
1) the above-mentioned halogen derivative used as a raw material is not easy to obtain because it is difficult to manufacture, PA1 2) because an equivalent reaction is involved the cost of synthesis is high, and PA1 3) a refining step is required because by-products occur. PA1 with a triarylamine compound having at least one triarylamine structure per molecule described by formula ##STR1## in the presence of platinum or platinum compound catalyst and a carboxylic acid compound; where each R is an independently selected hydrocarbon group selected from the group consisting of hydrocarbon groups comprising 1 to 10 carbon atoms and hydrocarbon groups comprising 1 to 10 carbon atoms in which at least one of the carbon atoms is bonded to a hetero-atom selected from the group consisting of O, N, F, Cl, Br, I, S, and Si; each R' is an independently selected hydrocarbon group comprising 1 to 10 carbon atoms; and n=0, 1, or 2; where the other bonds of the nitrogen atom are bonded to an aryl group. PA1 (a) A carboxylic acid, there are no particular restrictions as long as it has carboxyl groups. Examples include saturated carboxylic acids, unsaturated carboxylic acids, monocarboxylic acids, and dicarboxylic acids. A saturated or unsaturated aliphatic hydrocarbon group, aromatic hydrocarbon group, halogenated hydrocarbon group, hydrogen atom, or the like is usually selected as the portion other than the carboxyl groups in these carboxylic acids. PA1 (b) An anhydride of a carboxylic acid PA1 (c) A silylated carboxylic acid PA1 (d) A substance that will produce the above-mentioned carboxylic acid compounds of (a), (b), or (c) through a reaction or decomposition in the course of the hydrosilylation reaction in the present method.
A drawback to the hydrosilylation method is that a catalyst is needed, but in principle there are no by-products thus making this method a more desirable industrial process. There have been reports of methods for manufacturing a triarylamine having unsaturated groups by utilizing a hydrosilylation method. Even with this method, however, in actual practice the catalyst activity and the selectivity are low and oxygen must be added to the reaction atmosphere in order to prevent a decrease in the activity of the hydrosilylation catalyst. A number of problems are encountered in the hydrosilylation method such as (a) a large amount of catalyst is required and the reaction takes a long time, (b) reactions other than a hydrosilylation reaction can occur simultaneously forming polymers and producing oxides which lowers the yield, (c) the selectivity is low for the position where the addition is made in the hydrosilylation reaction and as a result the yield is low, (d) it is frequently difficult to separate and remove the by-products in the case of a low yield, and (e) there is the danger that the oxygen which it is often required to add will ignite and explode. Also because of the low selectivity for the position where the addition is made in the hydrosilylation reaction, a triarylamine having unsaturated groups obtained from this reaction will be a mixture of isomers. This mixture of isomers creates such problems as a difference among isomers in the decomposition and condensation rates of the hydrolyzable groups and a difference among isomers in the charge transfer capability due to varying ionization potential which is in turn due to different molecular structures.
An object of the present invention is to provide a novel method suited to the industrial production of a triarylamine having hydrocarbonoxysilyl groups by a hydrosilylation reaction. Specifically, an object is to solve the above identified problems (a) to (d) encountered with hydrosilylation reactions by increasing the activity of the platinum catalyst in a hydrosilylation reaction between a triarylamine compound having a vinyl group and a hydrido (hydrocarbonoxy)silane compound and improving the position selectivity thereby providing a method with which the targeted substance can be synthesized at a higher purity, at lower cost, and more efficiently. Another object is to provide a method in which the activity of the platinum catalyst is improved, which makes it possible for the hydrosilylation reaction to be conducted at a lower oxygen partial pressure or in an inert atmosphere and allows the danger of ignition and explosion during the hydrosilylation reaction to be avoided.
"Raising the position selectivity" here means that of the triarylamines having hydrocarbon oxysilyl groups that are the product, a triarylamine having a structure in which the hydrocarbonoxysilyl groups are bonded with aromatic rings via ethylene groups, that is, a .beta.-adduct with respect to an aromatic ring can be produced more efficiently than in the past.